Add Supabase Database to Next.js (Cursor Prompt)

Add Supabase database integration to this Next.js project.

FILES TO CREATE:
- src/lib/supabase/client.ts — Browser client (if not already created)
- src/lib/supabase/server.ts — Server client with cookies (if not already created)
- src/lib/supabase/admin.ts — Admin client using SERVICE_ROLE_KEY for server-only operations
- src/types/database.ts — Generated types from Supabase CLI (run: npx supabase gen types typescript --project-id YOUR_PROJECT_ID > src/types/database.ts)
- src/lib/queries/[resource].ts — Query functions per resource (e.g., getUsers, createPost, updatePost, deletePost)

QUERY PATTERN:
Every query function should:
1. Accept typed parameters
2. Use the typed Supabase client: supabase.from('table').select('*').returns<Row[]>()
3. Return { data, error } and handle errors with a consistent pattern
4. Be used in Server Components or Server Actions, NOT in client components directly

RLS POLICIES TO CREATE:
- Users can read their own data: auth.uid() = user_id
- Users can insert their own data: auth.uid() = user_id
- Users can update their own data: auth.uid() = user_id
- Users can delete their own data: auth.uid() = user_id
- Public read access where appropriate

DO NOT:
- Use the admin client in client-side code
- Skip RLS policies — every table must have RLS enabled
- Use raw SQL queries — use the Supabase query builder

ENVIRONMENT VARIABLES:
- NEXT_PUBLIC_SUPABASE_URL
- NEXT_PUBLIC_SUPABASE_ANON_KEY
- SUPABASE_SERVICE_ROLE_KEY (server only, never expose to client)